When it comes to user-side equipment in broadband fiber access, we often see terms such as OLT, ONU, ONT, SFU, and HGU. What are they? What’s the difference?
1. What is ONU and what is ONT?
The main application types of broadband optical access include: FTTH, FTTO and FTTB, and the user-side equipment has different forms under different application types.
The user-side equipment of FTTH and FTTO is used by a single user, which is called ONT (Optical Network Terminal).
The user-side equipment of FTTB is shared by multiple users, called ONU (Optical Network Unit).
The user mentioned here refers to the user independently billed by the operator, not the number of terminals used. For example, the ONT of FTTH is generally shared by multiple terminals in a home, but only one user can be counted.
2. Types of ONTs
ONT (Optical Line Terminal) is the modem, which is divided into SFU (Single Family Unit), HGU (Home Gateway Unit) and SBU (Single Business Unit).
2.1 SFU
SFU generally has 1 to 4 Ethernet interfaces, 1 to 2 fixed telephone interfaces, and some models also have cable TV interfaces. The SFU does not have the function of home gateway, the terminal connected through the Ethernet port can dial up to the Internet, and the remote management function is weak. The modem used in the early days of FTTH (Fiber to the Home) belongs to SFU and is rarely used at present.
2.2 HGU
The modems equipped by FTTH users opened in recent years are all HGUs. HGU usually comes with wifi and has a USB interface. Compared with SFU, HGU has the following advantages:
- HGU is a gateway device, which is convenient for home networking; while SFU is a transparent transmission device and does not have gateway capabilities. It generally needs the cooperation of gateway devices such as home routers in home networking.
- HGU supports routing mode, has NAT function, and is a layer-3 device; while SFU type only supports layer-2 bridge mode, which is equivalent to a layer-2 switch.
- HGU can realize its own broadband dial-up application, and the connected computers and mobile terminals can directly access the Internet without dial-up; while SFU must be dial-up by the user’s computer or mobile phone or other terminals, or dial-up through a home router.
- HGU is easier for large-scale operation and maintenance management.
2.3 SBU
SBU is mainly used for the access of FTTO users, generally with Ethernet interface, some models have E1 interface, fixed telephone interface, or with wifi function. Compared with SFU and HGU, SBU has better electrical protection performance and higher stability, and is also commonly used in outdoor occasions such as video surveillance.
3. Types of ONUs
The MDU is mainly used for the access of multiple residential users under the FTTB application type, and generally has at least 4 user-side interfaces, usually 8-way, 16-way, 24-way FE or FE+POTS (fixed telephone) interface.
The MTU is mainly used for the access of multiple enterprise users or multiple terminals in the same enterprise in the FTTB scenario. In addition to the Ethernet interface and the fixed telephone interface, the MTU may also have an E1 interface. The appearance and function of the MTU are generally the same as those of the MDU, but the electrical protection performance is better and the stability is higher. With the popularity of FTTO, the application scenarios of MTU are getting smaller and smaller.
4. ONT vs ONU
Both ONU and ONT are terminal devices to connect users in a passive optical network. Then, what is the difference?
- Deployment
ONT: An ONT is located at the customer premise (residential or commercial).
ONU: ONU can be placed in either the user’s home or the provider’s central office. - User
ONT: A single user uses the user-side equipment of FTTH and FTTO.
ONU: Multiple users share the user-side equipment of FTTB. - Categories
ONT: SFU, HGU, and SBU belong to ONT.
ONU: MDU and MTU belong to ONU. - Function
The ONU usually communicates with an ONT, which may be a separate box that connects the PON to TV sets, telephones, computers, or a wireless router.
An ONU converts optical signals to electrical signals via a fiber cable. An ONU organizes and optimizes different types of data coming from customers to efficiently send it upstream to the OLT (located at an ISP’s central hub).
5. Summary
Broadband optical fiber access mainly adopts PON (passive optical network) technology. When the specific form of user-side equipment is not distinguished, the user-side equipment of the PON system can be collectively referred to as ONU.
ONU, ONT, SFU, HGU… These all describe the user-side equipment of broadband access from different perspectives, and the relationship between them is shown in the following figure. Contact us (info@bonelinks.com) if you have any questions.
